(3ey) Study of Pressure Propagation Mechanism in the Multi-Plug Gelled Pipeline

Waxy crude oil gelation during its production, transportation, and storage in a deep subsea environment dramatically changes its flow characteristics. The challenges associated with long term production shutdown in this low temperature are considered to be a severe flow assurance problem, demands a high-pressure gradient to breakdown the gel structure and to restart normal operation. However, recent studies reported that enhanced gel compressibility allows enough deformation to break the gel structure and reduces the flow resistance. However, the gel compressibility is limited by the presence of dissolved gas which creates voids after crude oil gelation. Hence to artificial increase the compressibility we propose to remove some of the gelled material from the pipeline. Furthermore, the artificial compressibility is created in such a way that it produces a locally high-pressure gradient. Therefore, the present work focused on pressure propagation in a pipeline filled with high strength, weakly-compressible and thixotropic gel plugs separated by the gas pocket. A numerical model is developed to analyze the pressure propagation in the multi-plug gelled pipeline and to simulate the flow start-up process. The Volume of Fluid method is implemented to distinguish the two phases. The understanding of pressure propagation in a gelled pipeline is considered to be an important step of flow restart. In this direction, recent work revealed that pressure propagation and flow commencement in a pipe longer than critical length (L_c = ΔpR/2 τ_y where R is the radius of the pipeline, L_c is the critical pipe length, Δp is the applied pressure gradient and τ_y is the yield stress of the fluid) depends on the degree of deformation in the initial portion of the gel medium. If the initial deformation in the gel due to the combined effect of viscous and compressive deformation is higher than the critical deformation (yield strain), pressure may propagate and flow restart in a pipeline longer than a critical length. In the present case, the additional compressibility of the gas pocket further delays the pressure propagation and allowed to develop a high-pressure gradient sequentially across each gel segment. Figure 1 illustrates the different regimes of deformation as the pressure propagation develops a localized axial pressure gradient. In this localized high-pressure gradient, the gel plug degraded quickly and permit flow restart in a gelled pipe longer than the critical length.

Research Interests

My primary research interest is in the area of computational fluid dynamics, heat transfer, and multi-phase flow. Recent advancements in high-speed computing systems and solution algorithm support to unveil the physics lie within the fundamental flow processes. I strongly believe that scientific computing has provided new dimensions to uncover and understand the natural sciences.

In approaching my research interest I met Prof. Lalit Kumar at IIT Bombay, India who is working in the field of computational rheology and flow restart of waxy crude oil gelled in the subsea pipeline. Along with him, investigating the flow restart process with the objective of understanding the pressure propagation mechanism in order to estimate the reliable flow start-up pressure requirement. The analysis shows that gel degradation strongly depends on the local transient pressure gradient. The principal objective of my research work is to develop a reliable flow restart process. To achieve this, I have analyzed the flow restart process in a multi-plug gelled pipeline in which a single gel plug is divided into a number of smaller gel segments. Each gel segment is separated from the adjacent gel segments by compressible gases. The numerical analysis shows that the pressure propagation in the multi-plug pipeline is predominately controlled by gas compressibility. This results in a large pressure gradient developed across each gel segment sequentially. This high-pressure gradient is sufficient to overcome the gel resistance, breakdown the gel medium, and restart the normal operation.

In another work, the heat transfer process of the subsea pipeline filled with waxy crude oil is analyzed. In this analysis, the complication variation in physical property, gel strength, and expansion of gel structure is studied with temperature profile. The variation in gel properties in radial and axial direction are investigated.

As an organized scientific researcher, I would like to focus on computational rheology which includes heat transfer and multiphase flow. Additionally, I would like to develop a generalized elasto-viscoplastic thixotropic model for waxy crude gel based on my rheometric experience.